Stage 6 Maths Member

The Recipe Riddle

Everyday story · Teaches: Adding fractions with different denominators · Featuring Tryphonia

Tryphonia was baking with Grace. The recipe needed ½ a cup of flour, then ¼ a cup more. “How much flour altogether?” asked Grace.

“I cannot just add the top numbers,” said Tryphonia. “A half and a quarter are different sizes, they have different denominators (the bottom numbers).”

She had an idea. “Let me cut the half into quarters. One half is the same as two quarters.” Now both fractions were quarters: 2/4 + 1/4.

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This story teaches

Adding fractions with different denominators

Maths

Answer guide, for grown-ups

Ask each question, then compare. A child’s own words are perfect as long as the idea is right.

1. Why can you not just add ½ and ¼ straight away?

Because a half and a quarter are different sizes with different denominators (bottom numbers), so you cannot just add the top numbers.

✓ Understood if the child notes the fractions have different denominators or sizes.

2. How did Tryphonia change ½ so the fractions matched?

She cut the half into quarters, so one half became two quarters (2/4), matching the 1/4.

✓ Understood if the child says she changed 1/2 into 2/4.

3. What is a common denominator?

A common denominator is a shared bottom number that lets you add the fractions together.

✓ Understood if the child describes a shared bottom number for the fractions.

4. Work out 1/2 + 1/3 by making the denominators match.

Change them to sixths: 1/2 = 3/6 and 1/3 = 2/6, so 3/6 + 2/6 = 5/6.

✓ Understood if the child reaches 5/6 by using sixths.

Maths Moment: Change 1/3 into sixths: 1/3 = 2/6. Then 2/6 + 1/6 = 3/6, which is the same as 1/2.

For parents, Cambridge curriculum

Mapped to these Cambridge Primary objectives. Open a framework to verify.

Maths

Stage 6 · Number
Add and subtract fractions with different denominators using equivalence.
Verify in Cambridge Mathematics (0096) ↗